Foraminifers in the global stratotype (GSSP) of the Permian-Triassic boundary (Bed 27, Meishan, South China)

Abstract

The paper documents the results of a detailed study of the taxonomic composition and stratigraphic distribution of foraminifers in the Permian-Triassic transition bed (Bed 27) in the P-T GSSP (Bed 27, Meishan, South China). The earliest foraminiferal assemblage that followed the largest biotic crisis at the end of the Permian includes 15 genera of four orders, of which lagenids were the most abundant and diverse. The order Lagenida includes the following families: Pachyphloiidae (Pachyphloia), Geinitzinidae (Lunucammina s.l. (= Geinitzina = Neogeinitzina) and Robuloididae (Robuloides). In addition, the assemblage includes numerous members of the family Ichthyolariidae, the generic assignment of which needs confirmation: Frondinodosaria, Nodosinelloides, Protonodosaria, Tauridia, and Eocristellaria. Most recorded taxa occur in both Permian and Lower-Middle Triassic beds in the Tethyan Region and outside it, mainly in the middle, less commonly in the higher latitudes of the Northern and Southern Hemispheres. Apart from lagenids, a small proportion in the assemblages is represented by taxa of wide stratigraphic and geographical ranges (cosmopolitans) of the order Ammodiscida (Ammodiscus, Glomospiranella), and the order Globivalvulida (Globivalvulina), order Cornuspirida, family Neodiscidae (Neodiscus), family Hemigordiidae (Hemigordius, Hemigordiella) and a genus of uncertain affinity (Abriolina), typical of the Permian in the Tethyan Realm. The new results confirm previous records of foraminifers of the genera Lunucammina s.l., Pachyphloia, Robuloides, Nodosinelloides, Cryptoseptida, Globivalvulina, Hemigordius, and Ammodiscus in the P-T boundary bed in the Meishan section, and supplement the list of recorded taxa by Neodiscus, Abriolina, Eocristellaria, Tauridia, and Hemigordiellina. New results update the data on the diversity and abundance of foraminiferal shells in the sections as well as reveal some problems of their identifications. No significant biological innovations, changes in variability, or appearance of new taxa are registered immediately above the critical level at the P-T boundary, while the extinction of some survivors continued after the crisis.